Surface Sediment Distribution Research Articles

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A large number of sediment cores collected during 2005–2010 from the Taiwan Strait were analyzed for radionuclides ( 210Pb, 137Cs and 7Be) to elucidate sedimentation dynamics in this all-important gateway linking two largest marginal seas in the western Pacific (namely, the South China Sea and the East China Sea). Apparent sediment accumulation rates derived from 210Pb and 137Cs profiles vary from <0.1 to >2 cm/yr, averaging ∼0.4 cm/yr and showing a spatial pattern closely related to hydrodynamics and sediment source-to-sink pathways. Spatial-temporal variation of 7Be activity in surface sediments off Taiwan’s west coast indicates episodic deposition of flood layers and their mobility from river estuaries toward the north. In conjunction with particle size distribution in surface sediments and the structure of sediment strata revealed by sub-bottom echo images; the radionuclide data can be used to outline three different sediment source-to-sink dispersal systems. Based on sediment loads of surrounding rivers and the distribution of sediment accumulation rates, lateral transport is required to account for the budget and size distribution of sediments in the strait.

Spatial relationships between surface sedimentary facies distribution and topography using remotely sensed data: Example from the Ganghwa tidal flat, Korea

Spatial relationships between surface sedimentary facies distribution and topography, including channel networks and an intertidal digital elevation model (DEM), were estimated for the Ganghwa tidal flat, Korea. Tidal channels were extracted from high spatial resolution satellite data and used to derive maps of channel density and distance from channels. The intertidal DEM was generated by a waterline method using Landsat Enhanced Thematic Mapper Plus (ETM+) images, and the map of surface sedimentary facies distribution was produced from grain-size data on sediment samples. A GIS-based frequency ratio model was applied to quantify the relationships between the surface sediment facies and topographic factors. The result indicated that the fine-grained mud flat facies occurs mainly in areas of complex tidal channels and in elevated areas that have a high spectral reflectance in the Landsat ETM+ image. The coarse-grained sand flat facies is concentrated in areas of sparse tidal channels, and the mixed flat facies is distributed where tidal channels have an intermediate level of complexity. The results demonstrate a significant spatial relationship between the distribution of surface sediment in a tidal flat and topographic features. We conclude that tidal channels should be considered an important factor in mapping surface sedimentary facies in tidal flat environments, and that patterns of tidal topography are a useful adjunct to spectral reflectance in classifying sedimentary facies from remotely sensed data with high spatial resolution.

동해 울릉분지에서 대륙사면과 분지 퇴적물의 지화학적 특성에 따른 황산염 환원 비교

In conjunction with geochemical characteristics, rate of sulfate reduction was investigated at two sediment sites in the continental slope and rise (basin) of the Ulleung Basin in the East Sea. Geochemical sediment analysis revealed that the surface sediments of the basin site (D2) were enriched with manganese oxides (348 <TEX>${\mu}mol$</TEX> <TEX>$cm^{-3}$</TEX>) and iron oxides (133 <TEX>${\mu}mol$</TEX> <TEX>$cm^{-3}$</TEX>), whereas total reduced sulfur (TRS) in the solid phase was nearly depleted. Sulfate reduction rates (SRRs) ranged from 20.96 to 92.87 nmol <TEX>$cm^{-3}$</TEX> <TEX>$d^{-1}$</TEX> at the slope site (M1) and from 0.65 to 22.32 nmol <TEX>$cm^{-3}$</TEX> <TEX>$d^{-1}$</TEX> at the basin site (D2). Depth integrated SRR within the top 10 cm depth of the slope site (M1; 5.25 mmol <TEX>$m^{-2}$</TEX> <TEX>$d^{-1}$</TEX>) was approximately 6 times higher than that at the basin site (D2; 0.94 mmol <TEX>$m^{-2}$</TEX> <TEX>$d^{-1}$</TEX>) despite high organic content (>2.0% dry wt.) in the sediment of both sites. The results indicate that the spatial variations of sulfate reduction are affected by the distribution of manganese oxide and iron oxide-enriched surface sediment of the Ulleung Basin.

Clay mineral distribution in surface sediments of the northeastern South China Sea and surrounding fluvial drainage basins: Source and transport

Clay mineralogy of surface samples throughout the northeastern South China Sea (SCS) and surrounding fluvial drainage basins has been investigated to reveal source and transport of detrital fine-grained sediments. Three characteristic end-members in clay mineral compositions were observed from three major provenances, respectively: major kaolinite and moderate illite and chlorite from the Pearl River, predominant illite and chlorite from Taiwan, and principal smectite from the Luzon arc system. The transport of four clay mineral species in the northeastern SCS is influenced by various mechanisms. Smectite derived from the Luzon arc system is transported mainly by surface current with significant influence of the Kuroshio intrusion, illite and chlorite from Taiwan are mainly carried by deep water current, while kaolinite from the Pearl River is affected obviously by the westward Guangdong Coastal Current and longshore current. A westerly tongue-shaped distribution of high contents of illite and chlorite mainly from Taiwan on the eastern shelf may result from the westward Guangdong Coastal Current during the winter. The results suggest that clay mineral assemblages in the northeastern SCS are mainly controlled by provenance supply and current transport and their downcore records do not bear contemporaneous paleoclimatic features. The implication of clay minerals for proxies of the late Quaternary East Asian monsoon evolution is realized through both the provenance supply and current transport processes.

Impact of anthropogenic input on physicochemical parameters and trace metals in marine surface sediments of Bay of Bengal off Chennai, India

The study of heavy metal distribution in coastal surface sediments is an important component in understanding the exogenic cycling as well as in assessing the effect of anthropogenic influences on the marine ecosystem. In this study, surface sediment samples were collected from five different traverses along the innershelf of Bay of Bengal, off Chennai, India during pre- and post-monsoon seasons. The results of Spearmen correlation matrix, factor and cluster analysis, enrichment and contamination factor analysis, and geoaccumulation index of the heavy metals analyzed in the collected surface sediment were discussed. The level of both enrichment and contamination factor are shown in following order Cd > Cu > Cr > Ni > Pb > Co > Zn > Mn > Fe > Hg. The geoaccumulation index suggests that Cd and Cu are strongly to extremely pollute the sediments in both seasons. The results strongly indict anthropogenic sources for moderate input of Cd and Cu in to the innershelf of Chennai coast.

Dinoflagellate cyst distribution in surface sediments along the south-western Mexican coast (14.76° N to 24.75°N)

Abstract In this study, we explore the relationship between the modern assemblages of organic-walled dinoflagellate cysts and sea-surface conditions (temperature, salinity, primary productivity) and water depth and distance to the coast. Statistical treatments were performed on 95 surface sediment samples from sites located along the south-western Mexican coast (14.76° N to 24.75°N). Redundancy analysis (RDA) illustrates that the principal parameters correlated with the regional cyst distribution are the distance to the coast and the productivity in the upper water column, which is closely related to upwelling intensity. Empirical observations coupled with RDA provide insight into the spatial coverage of some cyst taxa produced by dinoflagellate species potentially responsible for harmful algal blooms along the coast. They also allow the recognition of four zones of assemblages, which are linked to the upwelling intensity and the productivity and characterize La Paz Bay, the south-western Mexican margin (from 15.95° N to 23.11° N), the northern part of the Gulf of Tehuantepec and the southern part of the Gulf of Tehuantepec.

Clay-mineral and grain-size distributions in surface sediments of the White Sea (Arctic Ocean): indicators of sediment sources and transport processes

In this study, the grain-size and clay-mineral compositions of 73 surface sediment samples collected in a variety of environmental settings in the White Sea are presented to characterize recent sedimentation processes, reconstruct transport pathways, and identify potential source areas of the terrigenous components. Areas >100 m deep are invariably characterized by silty clay, whereas areas <100 m deep exhibit more heterogeneous grain-size compositions plausibly explained by coastal erosion and (re-)distribution mechanisms, particularly tidal currents. The dominance of sand in the estuarine areas of the Onega and Dvina rivers as well as toward the Gorlo Strait connecting the White Sea with the Barents Sea is attributed to increased current speeds. Illite and smectite are the dominant clay minerals in recent sediments of the southwestern and eastern White Sea sectors, respectively. Their distribution patterns largely depend on the geology of the source areas, and mirror surface circulation patterns, especially in Dvina Bay. Smectite is a key clay mineral in White Sea surface sediments, as it reveals the dominating influence of the Northern Dvina’s runoff on sedimentation and water circulation throughout the basin. In comparison to other Eurasian shelf seas, the White Sea is characterized by a greater diversity of clay-mineral assemblages, which range from illite- to smectite-dominated sectors containing variable amounts of chlorite and kaolinite.

Lipid biomarkers in deep sea sediments from the Campos Basin, SE Brazilian continental margin

Lipid biomarker distributions in surface sediments were determined using gas chromatography (GC) and GC–mass spectrometry (GC/MS) in order to evaluate the sources and distribution of organic matter (OM) in the slope of Campos Basin (southeastern Brazilian continental margin). Samples were collected with a box corer at 43 stations ranging from 750 m and 1950 m water depth and in two sectors of the slope. The concentrations of total fatty acids [FAs; 111–2305 μg g total organic carbon (TOC) −1], total sterols (19.6–747 μg g TOC −1) and total n-alcohols (7.9–328 μg g TOC −1) represented a decreasing gradient in comparison to shallow areas (40–500 m) in the same region. The greater contribution of plankton-derived lipids (e.g. short chain FAs and alcohols, phytosterols) than lipids from terrestrial sources (long chain FAs and alcohols) suggested a predominance in the sediments of OM derived from autochthonous processes in the water column. In this sense, the sedimentary OM may represent a significant source of energy for secondary benthic producers. However, principal component analysis (PCA) and source assignment of lipids revealed variations in OM composition on a regional scale, which probably related to topographic features and local oceanographic conditions. Such differences in the composition, and consequently in the bioavailable fraction, of OM should be accounted for in the characterization of the benthic communities in the slope of the Campos Basin.

Quantitative estimation of intertidal sediment characteristics using remote sensing and GIS

High spatial resolution satellite data (IKONOS) combined with in situ data was used to quantitatively estimate the spatial distribution of tidal flat characteristics for the Hwangdo tidal flat, Cheonsu Bay, Korea. The classification result was accurate in terms of a comparison with the in situ data, and the overall accuracy was 90.7%, which confirmed the validity of the classification. GIS analysis based on a probabilistic model was applied to a quantitative estimation of the relationship between each surface sediment facies and the spectral reflectance. Mud flat facies showed a high positive correlation (R 2 = 0.91), and sand flat facies showed a high negative correlation (R 2 = 1.00), which was a good reflection of the sedimentary characteristics of Hwangdo tidal flat. Relationships between each sediment facies and DEM also showed good agreement with the topographic characteristics in the study area. The study revealed that intertidal surface sediment classification using high resolution remote sensing imagery and in situ data successfully shows spectral and topographic characteristics of the study area. It was noted that spectral reflectance was affected by a combination of environmental factors, including grain size, topography, and remnant surface water. It is possible to determine the type of tidal flat through quantitative estimates of the spatial distribution of surface sediments according to their spectral reflectance.

The effects of a winter upwelling on biogeochemical and planktonic components in an area close to the Galician Upwelling Core: The Sound of Corcubión (NW Spain)

To study the biogeochemical response and the coupling plankton–benthos to an unusual winter upwelling event a cruise was carried out in February 2005 in the Sound of Corcubión, near Cape Finisterre (NW Iberian Peninsula), the Galician upwelling core. This area represents the northern boundary of the Eastern North Atlantic Upwelling System (ENAUS). The spatial distribution of plankton assemblages (phytoplankton and zooplankton), chlorophyll, physical and chemical parameters as well as diatom distribution in surface sediments, were studied in a total of 17 stations in the Sound. The upwelling processes caused an important accumulation of water in the inner Sound and near the Cape. This accumulation zone must be persistent through the upwelling events in the area, including those of summer, as indicated by the diatoms' distribution in the sediment. Unlike the summer upwelling events, the main effect of winter upwelling in the area is the increase in solar radiation due to the persistent clear skies. In this season nutrient supply is not critical due to water column mixing. The meteorological conditions were equivalent to those of early spring. As a result, both phyto- and zooplankton species assemblages were typical of spring blooms in Galician coasts. The bloom lasted for up to 6 days, as estimated from the availability and uptake of nitrogen forms. Winter blooms represented ca. 20% of total annual phytoplankton biomass, and 30% of the average biomass during summer upwelling, in the period 1997–2007, as estimated from the analysis of both, in situ and satellite derived chlorophyll.

Clay mineral distribution in surface sediments of the South China Sea and its significance for in sediment sources and transport

Clay minerals of surface sediments in the South China Sea (SCS) are analyzed with X-ray diffraction, and their transport is explored with a grain size trend analysis (GSTA) model. Results show that clay mineral types in various sedimentary environments have different sediment sources and transport routes. Sediments in the northern SCS (north of 20°N) between the southwest of Taiwan Island and the outer mouth of the Pearl River have high contents of illite and chlorite, which are derived mainly from sediments on Taiwan Island and/or the Yangtze River. Sediments from the Pearl River are characterized by high kaolinite and low smectite content, and most are distributed in the area between the mouth of the Pearl River and northeast of Hainan Island and transported vertically from the continental shelf to the slope. Characterized by high illite content, sediments from Kalimantan Island are transported toward the Nansha Trough. Sediments from Luzon Island are related with volcanic materials, and are transported westwards according to smectite distribution. On the Sunda Shelf, sediments from the Mekong River are transported southeast in the north while sediments from the Indonesian islands are transported northward in the south. Ascertaining surface sediment sources and their transport routes will not only improve understanding of modern transportation and depositional processes, but also aid paleoenvironmental and paleoclimatic analysis of the SCS.

Diatom distribution in southeastern Pacific surface sediments and their relationship to modern environmental variables

The quantitative analysis of diatom assemblages preserved in 52 samples from the Bellingshausen and the Amundsen Seas provides the first comprehensive view on the distribution of diatoms in surface sediments of the eastern and central Pacific sector of the Southern Ocean. On a latitudinal transect along 120°W, diatom valve accumulation rates (AR) reach maximum values (8–10 × 10 8 valves m − 2 yr − 1 ) in a zone extending over ca. 900 km between the Antarctic Polar Front and the maximum average winter sea ice extent and exceed those ARs obtained from an eastern transect along 90°W by one order of magnitude. Lowest diatom concentrations (1–3 × 10 6 valves g − 1 ) were encountered in sediments of the Sea Ice Zone, affected by winter and summer sea ice. The accumulation rate pattern of the most abundant diatom Fragilariopsis kerguelensis (> 50% abundance in 47 samples) mirrors the pattern of the total diatom valve AR and the biogenic silica (BSi) AR, making F. kerguelensis the major contributor to the BSi preserved at the sea floor. Relative abundances of diatom species and species groups were statistically compared with a selection of environmental variables, such as the mean summer sea surface temperature and salinity, mean annual surface nutrient concentration (nitrate, phosphate, silicon), mean annual water column stratification, mixed layer depth in summer, and mean summer and winter sea ice concentrations. Polynomial canonical redundancy analysis (RDA) revealed the biogeographic distribution of diatom species had the strongest relationship with summer sea surface temperature (SSST) out of the nine tested environmental variables. This relationship accounted for 69.6% of the total variance of the diatom distribution, with 29.7% explained by the first gradient (significantly correlated to SSST with r 2 = 0.941) and 15.6% explained by the second gradient (correlated to both summer and winter sea ice and silicon concentration). Azpeitia tabularis, Hemidiscus cuneiformis and Roperia tesselata were associated with warmer water conditions (> 4 °C), whereas Fragilariopsis curta, F. separanda, F. rhombica and Thalassiosira gracilis were correlated with cold SSST (< 1.5 °C). Under the second gradient relationship, Actinocyclus actinochilus and F. curta were the most important diatoms representative of the diatom distribution in relation to the observed mean summer and winter sea ice concentrations. Confirming these environmental relationships is crucial for the development of reference data sets used in quantitative estimations of palaeoclimatic and palaeoceanographic conditions with statistical methods. This new data set represents the first modernised treatment of diatom remains from the SE Pacific Ocean and generally supports the use of a circum-polar database for the determination of summer SST, sea ice and potentially biogenic silica distribution of the Southern Ocean back into the Late Quaternary.

Regional influence of acid deposition and climate change in European mountain lakes assessed using diatom transfer functions

Summary1. Mountain lake sediments are valuable archives of environmental change. However, the presence of multiple drivers of change over similar or overlapping timescales may obscure palaeolimnological signals obtained using traditional statistical analyses.2. As part of the European Union‐funded EMERGE programme, sediment cores were obtained from 209 mountain lakes across 11 lake districts spanning gradients of altitude, latitude, geochemistry and atmospheric deposition. Surface sediments (0–0.5 cm) were subsampled to represent modern conditions corresponding with chemical and environmental measurements, while core bottom (15–17 cm) sediments were subsampled to represent the pre‐industrial period.3. We used a novel approach to explore the relative importance of environmental drivers of change in diatom communities. First, we used canonical correspondence analysis (CCA) to identify the most significant variables explaining diatom community distributions in lake surface sediments. Lake water pH, nitrate concentration/dissolved organic carbon (DOC) and ice‐free period were identified as uniquely significant explanatory variables along three primary axes of variation. The modern data set was then used to construct transfer functions linking diatom communities to these key variables. We applied these transfer functions to core bottom samples to reconstruct change since the pre‐industrial period.4. Drivers of diatom community change differed among regions. Diatom‐inferred pH declined in five acid‐sensitive lake districts (Central &amp; Southern Norway, Piedmont Ticino, Retezat Mountains, Scotland and Tatra Mountains), consistent with acidification caused by sulphur and nitrogen deposition. Diatom‐inferred pH increased in two lake districts [Julian Alps (JA), Pyrenees (PY)], probably due to eutrophication and climate warming‐induced increases in weathering rates respectively.5. Diatom inference models for nitrate and DOC were not independent. However, diatom‐inferred nitrate increased in all lake districts with detectable changes, except for the Retezat Mountains. These changes are consistent with increased nitrogen deposition and leaching in the industrial period and are independent of acidification effects, presumably reflecting a nitrogen fertilization effect. Diatom‐inferred DOC increased in the Central Alps and Scotland but decreased in Central Norway and Northern Finland, in contrast to increasing trends reported for Northern Europe and North America over the last 10–20 years. Conflicting drivers of change in DOC such as recovery from acidification and climate change further confound the interpretation of diatom‐inferred changes.6. Changes in the diatom‐inferred ice‐free period varied across regions. Warming is indicated in Central Norway, Scotland, Piedmont Ticino and the Pyrenees, while cooling is suggested in the more southern and eastern Julian Alps and Rila Mountains. Where detectable changes in diatom‐inferred pH and ice‐free period coincide there is generally an association between acidification and climate warming. Since warming is associated with increased weathering and alkalinity generation it is therefore possible that climate warming has reduced the impacts of acidification in acid‐sensitive lake districts.

Origin and distribution of surface sediments in the Grgur Channel, Adriatic Sea, Croatia

Granulometrical, mineralogical and morphological investigation of the sea-bottom sediments in the Grgur Channel revealed five sediment types; the most frequent of them are muds containing some amount of coarse sediment fractions (sand and gravel). The coarsest fractions are prevalently composed of recent shell fragments. Unexpected well rounded carbonate gravel was found SE of the Prvic Island at 83 m of water depth. This gravel was presumably transported, shaped and deposited during a lowstanding sea-level by stream and/or in beach environment. Fine-grained fractions have siliciclastic composition and show a prevalenty terrigenous origin. One part of the fine-grained fraction originates from recent subaerial weathering of flysch outcrops and the other from subaerial erosion of presently submerged flysch outcrops active during a lower sea-level. Due to the rapid Late Pleistocene-Holocene transgression, the investigated sediments are now below the present wave-base. Due to the presumed very low or even negligible recent sedimentation in the study area, older sediments in the Grgur Channel remain uncovered and mixed by burrowing organisms. Therefore, analyzed surface sediments from the Grgur Channel are considered as a mixture of recent and subrecent deposits. By this investigation, a new seabed sediments map of the Grgur Channel was produced, as an improvement of the existing sedimentological map of the Kvarner area.

Dinoflagellate cyst distribution in marine surface sediments off West Africa (17–6°N) in relation to sea-surface conditions, freshwater input and seasonal coastal upwelling

An organic-walled dinoflagellate cyst analysis was carried out on 53 surface sediment samples from West Africa (17–6°N) to obtain insight in the relationship between their spatial distribution and hydrological conditions in the upper water column as well as marine productivity in the study area. Multivariate analysis of the dinoflagellate cyst relative abundances and environmental parameters of the water column shows that sea-surface temperature, salinity, marine productivity and bottom water oxygen are the factors that relate significantly to the distribution patterns of individual species in the region. The composition of cyst assemblages and dinoflagellate cyst concentrations allows the identification of four hydrographic regimes; 1) the northern regime between 17 and 14°N characterized by high productivity associated with seasonal coastal upwelling, 2) the southern regime between 12 and 6°N associated with high-nutrient waters influenced by river discharge 3) the intermediate regime between 14 and 12°N influenced mainly by seasonal coastal upwelling additionally associated with fluvial input of terrestrial nutrients and 4) the offshore regime characterized by low chlorophyll-a concentrations in upper waters and high bottom water oxygen concentrations. Our data show that cysts of Polykrikos kofoidii, Selenopemphix quanta, Dubridinium spp., Echinidinium species, cysts of Protoperidinium monospinum and Spiniferites pachydermus are the best proxies to reconstruct the boundary between the NE trade winds and the monsoon winds in the subtropical eastern Atlantic Ocean. The association of Bitectatodinium spongium, Lejeunecysta oliva, Quinquecuspis concreta, Selenopemphix nephroides, Trinovantedinium applanatum can be used to reconstruct past river outflow variations within this region.

A Finnish chironomid- and chaoborid-based inference model for reconstructing past lake levels

In the present study I utilize subfossil chironomid and chaoborid distributions in surface sediments of 68 shallow lakes. The aim is to develop a calibration model for past water-level reconstructions by applying weighted averaging-partial least squares (WA-PLS) techniques and to evaluate its potential applications and limitations. This study considers water depth at sampling sites, rather than maximum lake depth. The best of the water depth models developed uses three components and has a cross-validated coefficient of determination ( r 2 jack) of 0.68 and root-mean-squared error of prediction (RMSEP) of 0.78 m. The model performance is tested on the sediment sequence of a previously studied lake from southern Finland that is known to have experienced past fluctuations in its water level. The water levels inferred are compared with results of chironomid-inferred air temperature reconstruction to ease separation of the effects of the variables. The reconstruction shows consistent results similar to those of previously published cladoceran planktonic:littoral ratios (P:Ls) from the same lake. However, the results indicate that factors other than depth and temperature, such as pollution, may possibly distort the inference results. The results suggest that in applying the midge-based water depth calibration model, it would be advantageous to use it together with an inference model for temperature and preferably in a multiproxy content where changes in water chemistry may be detected. The model can be useful in studies on past effective moisture variability that is closely related to climatic changes.

Changes in bedload transport rate associated with episodic sediment supply in a Japanese headwater channel

Abstract We conducted field monitoring of bedload transport rate associated with experimental sediment release in a natural channel to clarify behavior of the supplied sediment on mixed size bed. Observation of bedload rate at two sites along the 30 m channel reach revealed that downstream migration of finer particles delay compared with coarser particles. Ratio of the bedload sediment that deposited during the migration was higher for finer sediments. These behaviors of the mixed size particles were clear during passage of the sediment wave without changes in water discharge. Flashing peak of discharge that caused artificially by opening of the dam gate did not destroy channel bed structure including steps and pools formed by coarser sediments, and only small amount of bedload was mobilized. Both reach scale channel features including steps, pools, and riffles as well as fine scale features (i.e., armour coat) likely increased critical shear stress of particles and decreased bedload rate during our experiment. Extreme sediment supply induced two types of sediment deposition; (1) filling the pools in reach sales and (2) the intrusion of fine particles into the coarser sediment that formed an armour layer. The all grain size fractions can deposit as type (1) when shear stress of stream water is not enough to entrain bedload particles, while deposition type (2) occurs when finer sediment pass over channel bed on which armour coat is well-developed. Deposition of finer sediment into coarser sediment that forms armour coat is affected by grain size distribution of bed surface sediment. Thus, impact of the sediment supply on downstream channel depends on both bedforms and grain size distribution of bed surface sediment over which the supplied sediment pass.

Sources and spatial distribution character of n-alkanes in surface sediments of Nam Coon the Tibetan Plateau

通过测定纳木错现代植物和表层沉积物样品中的正构烷烃,结合主成分分析方法,明确了表层沉积物中烷烃的主要来源,并初步分析了它们在湖泊中的空间分布特征.研究结果显示,沉水植物所含烷烃以n-C₂₁-C₂₅为主,具有n-C₂₃的峰值;陆生植物主要含n-C₂₇-C₃₃烷烃,具有n-C₂₉或n-C₃₁的峰值;但垫状点地梅(Androsace tapete)和香柏(Sabina pingii)的主峰碳却是n-C₃₃烷烃,这在以往研究中鲜有报道.在纳木错表层沉积物中,正构烷烃具有典型的n-C₃₁和n-C₂₃双峰分布形式,来源于低等菌藻类、沉水植物以及陆生植物.其中碳数小于C₂₀的短链烷烃主要来源于低等菌藻类,其空间分布均一,由低等菌藻类的浮游生活型所决定;长链烷烃主要来源于高等植物,含量从滨岸到湖中心逐渐减少,这与其在运移和沉积过程中受微生物的持续降解作用有关.此外,来源于陆生植物的n-C₂₇-C₃₃烷烃因河流汇水面积和流量不同而存在空间差异,这值得重视和进一步研究.;Aquatic and land plants as well as surface sediments from Nam Co in Tibetan Plateau were collected and n-alkanes analysishad been conducted to identify the sources and spatial distribution of these molecular. The results indicated that n-alkanes rangingfrom 21 to 25 were identified to be derived from submerged plants, while n-alkanes ranging from 27 to 33 with n-C₂₉ or n-C₃₁peakwere derived from land plants except Androsace tapete and Sabina pingii. These two species contain n-alkanes with n-C₃₃ peak whichwere seldom reported before. Combined with information on plant sources and principal component analyses, three distinct groups ofn-alkanes with different spatial distribution in surface sediments were defined. Short-chain n-alkanes derived from photosyntheticbacteria and algae were relatively uniform in whole lake. But concentration of long chain n-alkanes gradually reduce from lake shoreto center coincided with transport distance increasing, indicating the main controlling mechanism of spatial distributions in surfacesediments was connected with biodegradation.

Patterns of surface sediment grain size distribution under the influence of varying wave conditions on a mixed sediment beach at Pevensey Bay, southeast England

Surface sediment distributions, derived using a new DGPS based survey technique, are described from three sections of a mixed sediment beach (MSB) at Pevensey Bay, southeast England. Spatial patterns of the distribution and size composition are related to antecedent hydrodynamic conditions and beach topography. Results indicate that higher energy waves produce a beach surface with a relatively homogenous grain size distribution, whilst lower energy waves produce surfaces with a more mixed size distribution. Under storm conditions, a 'type' beach response was recorded, comprised of a fine upper beach face and coarse lower beach face. Management practices, especially beach renourishment, also influence beach surface sediment distribution patterns

Origin and distribution of surface sediments and human impacts on recent sedimentary processes. The case of the Amvrakikos Gulf (NE Ionian Sea)

The sedimentology of the floor of the Amvrakikos Gulf, a river influenced, semi-enclosed relatively shallow-silled embayment, lying along the northeastern Hellenic coast of the Ionian Sea (eastern Mediterranean Sea), is investigated with respect to its origin (terrigenous and/or biogenic), the prevailing oceanographic conditions and human interference. Nearshore (water depths approximately <10 m) sediments, especially along the northern margin of the Gulf, consist mostly of biogenic sands, as the result of water exchange between the freshwater lagoonal waters and the surface waters of the Gulf. An exception to this is the mouth area of the Arachthos River, which is dominated by the terrigenous riverine sediment influx. The offshore (water depths >10 m) bottom surficial sediments are fine-grained (silty and clayey) of terrigenous origin (>70%); this is attributed to the inter-seasonal, strong two-layer stratification of the water column in the Gulf which restricts benthic productivity by inhibiting the downward flux of surface eutrophic waters and the development of nearbed disoxic conditions in water depths >40 m. River damming has reduced also the riverine terrigenous sediment supply; this is more profound in the case of the Arachthos River where not only the deltaic evolution has been affected, but also the textural character of the seabed sediments of the mouth area has been altered; this is expected to influence the benthic communities of prodeltaic surficial sediment.